Both are dongles, $179 against $250. This page puts them side by side on the only three things a maker can be held to — power, output impedance and noise — and then asks the question that actually matters: which headphones do they treat differently?
The Questyle M15 reaches 100 dB on 565 of the 567 models here, the Astell&Kern HC3 on 561.
| Specification | Astell&Kern HC3 | Questyle M15 |
|---|---|---|
| Power into 32Ω | 125 mW | 300 mW |
| Power into 150Ω | 27 mW | 110 mW |
| Power into 300Ω | 13 mW | 55 mW |
| Power into 600Ω | 6.7 mW | 28 mW |
| Output impedance | 2.0 Ω | 0.5 Ω unverified |
| Output noise | not published | 3 µV unverified |
| Price | $179 | $250 |
| Headphones it reaches 100 dB on out of 567 | 561 | 565 |
A figure marked not published is missing from the maker’s own material, which is not the same as being good or bad. Where one of these two publishes a number and the other does not, the comparison on that axis cannot be made at all — and saying so is more useful than guessing.
| Load | Astell&Kern HC3 | Questyle M15 |
|---|---|---|
| 32 Ω | Upper bound | Unverified |
| 150 Ω | Upper bound | Unverified |
| 300 Ω | Upper bound | Unverified |
| 600 Ω | Upper bound | Unverified |
Questyle M15 publishes no electrical specification at all. That is true of 10 of the 280 sources here, and the figures in that column come from independent measurement rather than from a maker document — which is not worse, but it is not the same thing, and it cannot be checked against anything the maker will stand behind.
The Astell&Kern HC3 column stands on something its maker printed, but not on a power rating: those figures are ceilings worked out from a maximum output voltage. Reading the two straight across sets one kind of claim against another, and nobody has written down the conditions of both side by side.
What each of these labels means, and why a derived figure is still worth printing, is set out in how this data was built.
4 headphones reach 100 dB on the Questyle M15 but not on the Astell&Kern HC3 — Moondrop COSMO, Symphonium Crimson, Symphonium Helios, 1 more.
561 of the 567 models here reach 100 dB on both. That is a power count and nothing more; whether either source suits a given headphone also depends on the two lines above.
The counts above say how many models the two treat differently. This says by how much. The same 8 headphones appear on every page of this kind, ordered from the easiest to drive to the hardest, so a row can be read across pages as well as across columns. Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Audio-Technica ATH-R70X: Questyle M15 has +13 dB of headroom there against +7 dB. 6 dB is about 4.2 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Astell&Kern HC3 and Questyle M15 because neither maker publishes no output noise figure. That is a gap in the specification, not a quiet amplifier, and it is left blank here rather than filled with a plausible number.
| Headphone | Impedance | Needs | Astell&Kern HC3 headroom | Questyle M15 headroom | Astell&Kern HC3 hiss | Questyle M15 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +29 dB damping | +33 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +9 dB damping | +13 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +19 dB | +23 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +14 dB | +20 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +11 dB | +15 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +7 dB | +13 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +3 dB | +9 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +1 dB | +6 dB | not published | not published |
The Questyle M15 costs $71 more than the Astell&Kern HC3. Out of the 567 models here, that difference buys 4 more models driven to 100 dB.
Nothing runs the other way: there is no axis here on which the cheaper of the two does better.
Everything in this paragraph counts only figures the two makers published. An advantage on an axis one of them leaves blank cannot be counted, and is not counted — how often that happens is its own page.
Each has a page of its own with a full headphone list and the provenance of every figure — worth opening here, because Questyle M15 has published no electrical specification at all and everything above comes from independent measurement: Astell&Kern HC3 and Questyle M15. Or put either against your own headphones in the source comparison tool.